This invention relates in general to accumulated material bead bypass and web control systems and, more particularly, their use in an improved photoelectrophoretic imaging system.
In the photoelectrophoretic imaging process, monochromatic including black and white or full color images are formed through the use of photoelectrophoresis. An extensive and detailed description of the photoelectrophoretic process is found in U.S. Pat. Nos. 3,384,488 and 3,384,565 to Tulagin and Carreira; 3,383,993 to Yeh and 3,384,566 to Clark, which disclose a system where photoelectrophoretic particles migrate in image configuration providing a visual image at one or both of two electrodes between which the particles suspended within an insulating carrier is placed. The particles are electriically photosensitive and are believed to bear a net electrical charge while suspended which causes them to be attracted to one electrode and apparently undergo a net change in polarity upon exposure to activating electromagnetic radiation. The particles will migrate from one of the electrodes under the influence of an electric field through the liquid carrier to the other electrode.
The photoelectrophoretic imaging process is either monochromatic or polychromatic depending upon whether the photosensitive particles within the liquid carrier are responsive to the same or different portions of the light spectrum. A full-color polychromatic system is obtained, for example, by using cyan, magenta and yellow colored particles which are responsive to red, green and blue light respectively.
In photoelectrophoretic imaging generally, and as employed in the instant invention, the important broad teachings in the following four paragraphs should be noted.
Preferably, as taught in the four patents referred to above, the electric field across the imaging suspension is applied between electrodes having certain preferred properties, i.e., an injecting electrode and a blocking electrode, and the exposure to activating radiation occurs simultaneously with field application. However, as taught in various of the four patents referred to above and Luebbe et al. U.S. Pat. No. 3,595,770; Keller et al. U.S. Pat. No. 3,647,659 and Carreira et al. U.S. Pat. No. 3,477,934; such a wide variety of materials and modes for associating an electrical bias therewith, e.g., charged insulating webs, may serve as the electrodes, i.e., the means for applying the electric field across the imaging suspension, that opposed electrodes generally can be used; and that exposure and electric field applying steps may be sequential. In preferred embodiments herein, one electrode may be referred to as the injecting electrode and the opposite electrode as the blocking electrode. This is a preferred embodiment description. The terms blocking electrode and injecting electrode should be understood and intepreted in the context of the above comments throughout the specification and claims hereof.
It should also be noted that any suitable electrically photosensitive particle may be used. Kaprelian, U.S. Pat. Nos. 2,940,847 and Yeh, U.S. 3,681,064 discloses various electrically photosensitive particles, as do the four patents referred to above.
In a preferred mode, at least one of the electrodes is transparent, which also encompasses partial transparency that is sufficient to pass enough electromagnetic radiation to cause photoelectrophoretic imaging. However, as described in Weigl, U.S. Pat. No. 3,616,390 both electrodes may be opaque.
Preferably, the injecting electrode is grounded and the blocking electrode is biased to provide the field for imaging. However, such a wide variety of variations in how the field may be applied can be used, including grounding the blocking electrode and biasing the injecting electrode, biasing both electrodes with different bias values of the same polarity, biasing one electrode at one polarity and biasing the other at an opposite polarity of the same or different value, that just applying sufficient field for imaging can be used.
The photoelectrophoretic imaging system disclosed in the above-identified patents may utilize a wide variety of electrode configurations including a transparent flat electrode configuration for one of the electrodes, a flat plate or roller for the other electrode used in establishing the electric field across the imaging suspension.
There has been recently developed a photoelectrophoretic imaging system which utilizes web materials, which optimally may be disposable. In this process, the desired, e.g., positive image, is formed on one of the webs and another web will carry away the negative or unwanted image. The positive image can be fixed to the web upon which it is formed, or the image transferred to a suitable backing such as paper. The web which carries the negative image can be rewound and later disposed of. In such photoelectrophoretic imaging system employing disposable webs, cleaning systems are not required.
In photoelectrophoretic imaging systems employing a web device configuration, it is desirable to remove any accumulation of excess liquid build-up at the line of contact between the web and the other surface (which may be a web) to prevent bead material, at the trailing edge of an image, from flowing or otherwise extending into web areas to be used for subsequent images and thereby degrading the quality of subsequent images.
Apparatus in which surfaces including web materials are moved into and out of intimate pressure engagement for processing of film is generally known. For example, U.S. Pat. No. 3,640,204 to Gordon discloses a web processing device in which a web containing a processing ingredient or solution is brought into pressure engagement with an exposed film to effect processing of the film. This patent is not concerned with the problems overcome by the present invention, e.g., eliminating accumulation of bead material at the line of contact between the web and surface.
A process for removing excess liquid developer from a photoconductive surface is the Pneumatic Assembly Liquid Removing method and apparatus disclosed by Smith et al. in U.S. Pat. No. 3,741,643. In this pneumatic assembly liquid removing process, a system is provided wherein excess toner is removed from the photoconductive surface by means of apparatus that requires equipment that is expensive and complex in comparison with the instant invention.
In Mihajlov, U.S. Pat. No. 3,281,241, a bead of developer liquid is advanced across the surface of the imaging support member. There is no suggestion, however, for employing the techniques of the instant invention.
In earlier photoelectrophoretic apparatus which sometimes encounters this bead of accumulated material, Egnaczak, U.S. Pat. Nos. 3,673,632 and Riley, 3,686,035 provide a slot in one of the surface to collect a bead, the slot being periodically emptied, to solve a similar problem. However, it may be impossible or impractical to employ a similar arrangement when using relatively thin webs as the surfaces.
One system that provides a simple and economical method and apparatus to eliminate this tailing liquid problem, without the above noted disadvantages, is disclosed in the copending application Ser. No. 476,189 entitled Bead Bypass by Herman A. Hermanson, filed on the same date and assigned to a common assignee. In this system, apparatus is employed to separate two surfaces to a spacing sufficient to allow accumulated bead material formed at the line of contact between the surfaces to pass therebetween. However, when separation occurs, there may be a change in web velocity due to corresponding changes in web length. This change in web velocity or web length may be reflected at other process steps that are being carried out contemporaneously in the system.